As is known in the art, waveguide structures may be fed with a feed line. For example, as show in FIG. 1, a suspended air stripline (SAS) 10 may be disposed in a waveguide 12 leading to an aperture of an antenna (not shown). Such feed lines typically operate over a relatively narrow bandwidth and with a single polarization.
As is also known, there is a trend in radio frequency (RF) systems to operate with multi spectra (i.e. multi frequency) polarimetric signal processing. Thus, current feed lines used in waveguide structures limit the ability to provide multi-spectral signal processing systems.
In certain applications, multiple feed lines have been provided in a microstrip configuration by using multiple conductors having a relatively lossy dielectric material disposed therebetween. The use of laminated conductors has also been proposed as a way to reduce losses due to conduction current and ohmic losses in the conductors. The laminating thickness is smaller or on the order of the skin depth of the conductor.
FIG. 2, illustrates a prior art microstrip transmission structure 14 provided from multiple laminated conductors which form a composite conductor. The transmission structure is provided from a polystyrene substrate 16 having a ground plane 18 disposed over a first surface thereof and a conductor 20 disposed over a second, opposite surface thereof. Four (4) layers 22a-22d of lossy dielectric material (e.g. Rogers 6002) are disposed over conductor 20 with each layer 22a-22d having a conductor 24a-24d disposed thereover.
This structure has reduced ohmic loss in the microstrip conductors compared with the ohmic losses which occur in prior art microstrip structures provided from a single solid conductor. While such an approach shows some improvement compared with prior art approaches, increased improvement is still required in many applications.